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| United States Patent |
5,552,149
|
|
Lebo, Jr.
, et al.
|
September 3, 1996
|
Method for microencapsulation of agriculturally active substances
Abstract
A method for microencapsulating agriculturally active substances such as
pesticides to provide improved resistance to environmental degradation,
especially ultra-violet light. The method employs as the UV protectant
lignosulfonates, such as sulfite lignin or sulfonated lignin, or
alternately sulfonated lignite, sulfonated tannins, napthalene sulfonates
or other related compounds in combination with a protein such as a high
bloom gelatin to form a capsule wall. The capsule wall formed by the
interaction of these components is durable and has an ultra-violet
protectant as an integral part of its structure.
| Inventors:
|
Lebo, Jr.; Stuart E. (Schofield, WI);
Detroit; William J. (Schofield, WI)
|
| Assignee:
|
Lignotech USA, Inc. (Rothschild, WI)
|
| Appl. No.:
|
133896 |
| Filed:
|
October 12, 1993 |
| Current U.S. Class: |
424/408; 252/589; 264/4.1; 264/4.3; 424/93.1; 424/93.46; 424/93.6; 424/418; 504/359 |
| Intern'l Class: |
A01N 025/34; B01J 013/10; B01J 013/20 |
| Field of Search: |
252/589
264/4.1,4.3,4.7
514/963
424/408,491,418
71/DIG. 1
|
References Cited
U.S. Patent Documents
| Re29238 | May., 1977 | Dimitri et al. | 71/101.
|
| 2090109 | Aug., 1937 | Coe | 427/407.
|
| 2800458 | Jul., 1957 | Green | 264/4.
|
| 3242051 | Mar., 1966 | Hiestand et al. | 264/4.
|
| 3505254 | Apr., 1970 | Kidwell et al. | 523/202.
|
| 3839561 | Oct., 1974 | Bordenca | 424/174.
|
| 4007258 | Feb., 1977 | Cohen et al. | 71/DIG.
|
| 4056610 | Nov., 1977 | Barber, Jr. et al. | 424/419.
|
| 4094969 | Jun., 1978 | Batzer et al. | 424/78.
|
| 4184866 | Jan., 1980 | DelliColli et al. | 71/65.
|
| 4223007 | Sep., 1980 | Spence et al. | 424/418.
|
| 4244728 | Jan., 1981 | DelliColli et al. | 71/65.
|
| 4244729 | Jan., 1981 | DelliColli et al. | 71/65.
|
| 4280833 | Jun., 1981 | Beestman et al. | 71/100.
|
| 4344857 | Aug., 1982 | Shasha et al. | 504/244.
|
| 4402856 | Sep., 1983 | Schnoring et al. | 71/DIG.
|
| 4417916 | Nov., 1983 | Beestman et al. | 71/93.
|
| 4497793 | Feb., 1985 | Simkin | 264/4.
|
| 4557755 | Dec., 1985 | Takahashi et al. | 264/4.
|
| 4753799 | Jun., 1988 | Nelsen et al. | 424/408.
|
| 4808408 | Feb., 1989 | Baker et al. | 424/408.
|
| 4844896 | Jul., 1989 | Bohm et al. | 424/89.
|
| 4846888 | Jul., 1989 | Detroit | 106/93.
|
| 4938797 | Jul., 1990 | Hasslin et al. | 71/118.
|
| 5023024 | Jun., 1991 | Kyogoku et al. | 264/4.
|
| 5292533 | Mar., 1994 | McMahon et al. | 424/408.
|
| Foreign Patent Documents |
| 0025379 | Aug., 1979 | EP.
| |
| WO92/19102 | Feb., 1992 | WO.
| |
Other References
"What's New in the Ever-Changing World of Micro and Macroencapsulation",
Suzanne Christiansen, Soap/Cosmetics/Chemical Specialties, Sep., 1992, pp.
26-28.
|
Primary Examiner: Lovering; Richard D.
Attorney, Agent or Firm: Andrus, Sceales, Starke & Sawall
Claims
I claim:
1. A method for encapsulating an ultra-violet sensitive agriculturally
active pesticide in a protective capsule wall, comprising the steps of:
dissolving a protein and an ultra-violet protectant selected from the group
consisting of a lignosulfonate, a sulfonated lignite, a sulfonated tannin,
a naphthalene sulfonate, a condensed naphthalene sulfonate and an
azolignosulfonate in a solution;
mixing a pesticide in said solution to form an emulsion;
coacervating the emulsion to form capsules having a protein/ultra-violet
protectant complex as a capsule wall; and
recovering the capsules.
2. The method of claim 1 wherein the pesticide is a pyrethroid.
3. The method of claim 2 wherein the pyrethroid is selected from the group
consisting of allethrin, cyfluthrin, cypermethrin, fenothrin,
flucythrinate and indothrin.
4. The method of claim 1 wherein the pesticide is an organophosphonate.
5. The method of claim 4 wherein the organophosphonate is selected from the
group consisting of crufomate, dursban, dicrotphos, parathion and phorate.
6. The method of claim 1 wherein the pesticide is pyrethrum.
7. The method of claim 1 wherein the pesticide is selected from the group
consisting of a virus, a bacterium, a nematode and a fungi.
8. The method of claim 1 wherein said pesticide is a nuclear polyhedrosis
virus and is selected from the group consisting of Heliothis zea, H.
virescens, Lymantrai dispar, Orgai pseudotsugata, Neodiprion sertifer, and
Autographa californica.
9. The method of claim 1 wherein said pesticide is a bacterium and is
selected from the group consisting of Bacillus thuringiensis, Bacillus
sphaericus, Bacillus popilliae, and Bacillus cereus.
10. The method of claim 1 wherein said pesticide is a nematode and is
selected from the group consisting of Neoaplectana carpocapsae,
Octomyomermis muspratti, Steinemema carpocapsae and Romanomermis
culiciuora.
11. The method of claim 1 wherein said pesticide is a fungi and is selected
from the group consisting of Verticillium lecanii and Entomophthora genus.
12. The method of claim 1 wherein said protein is selected from the group
consisting of albumin, agar-agar, algen, gluten, casein, fibrin and
gelatin.
13. The method of claim 1 wherein the ultra-violet protectant is modified
to have increased ultra-violet absorbance in the 290-400 nm range.
14. A process for preparing encapsulated pesticides comprised of the
following steps:
i. dissolving a protein selected from the group consisting of albumin,
agar-agar, algen, gluten, casein, fibrin and gelatin, and an ultra-violet
protectant selected from the group consisting of a lignosulfonate, a
sulfonated lignite, a sulfonated tannin, a naphthalene sulfonate, a
condensed naphthalene sulfonate and an azo-lignosulfonate, in a solution
having a pH of about 6.0 to 8.5;
ii. emulsifying a pesticide in said solution;
iii. acidifying the resulting emulsion to a pH close to the isoelectric
point of the protein by controlled addition of acid to form a coacervated
mixture containing a protein/ultra-violet protectant complex as a capsule
wall;
iv. transferring the coacervated mixture to a chilled water bath; and
isolating said capsules.
15. The process of claim 14 further including the step of hardening the
capsule wall prior to isolating said capsules.
16. The process of claim 15 wherein the step of hardening comprises adding
a crosslinking agent to said chilled water bath.
17. The process of claim 16 wherein the crosslinking agent is selected from
the group consisting of formaldehyde, acetaldehyde, glyceraldehyde,
malonic acid dialdehyde and glyoxal.
18. The process of claim 14 wherein the step of isolating said capsules
comprises filtration.
19. The process of claim 14 further including the step of neutralizing said
coacervated mixture prior to isolating said capsules.
Description
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a method for microencapsulating
agriculturally active substances and, more specifically, to the production
of microencapsulated chemical and/or biological actives having improved
resistance to environmental degradation, especially that caused by
exposure to ultra-violet (UV) light. Said actives can be any UV sensitive
synthetic or natural or biologically derived pesticide.
The use of microencapsulation as a means of controlling the release of
actives, of improving handling via reduced toxicity and of improving
environmental stability has been documented. Without such protection, the
effectiveness of such actives can be drastically reduced by numerous
factors including volatilization and degradation caused by exposure to
ultra-violet light. By use of the process described herein, the resistance
of UV sensitive chemical and/or biological actives to such losses can be
greatly reduced.
2. Prior Art
A number of microencapsulation systems have been proposed for prodding
protection of agriculturally active substances.
One method suggested in U.S. Pat. No. 3,839,561 utilizes diisophorone
derivatives to protect active cyclopropane carboxylic acid compounds from
ultra-violet induced degradation. Similarly, U.S. Pat. No. 4,094,969
describes the use of a sulfonated copolymer of catechin and leucocyanidin
as a UV stabilizer. In both cases, however, the formulations suggested do
not maintain the sunscreen and active in close enough contact to be
effective.
In U.S. Pat. No. 3,242,051, a method for coating materials by phase
separation is described. Gelatin and various carboxylated polymers such as
gum acacia and ethyl cellulose are used to form the coating. The use of a
similar ethylcellulose/gelatin system is described by Ignoffo and Batzer
in "Microencapsulation and Ultraviolet Protectants to Increase Sunlight
Stability of an Insect Virus", J. of Econ. Entomology, Vol. 64, pp.
850-853 (1966), and the use of a chlorophyll green/gelatin system is
described in U.S. Pat. No. 2,090,109. In these cases, however, the
materials have less than desirable environmental stability. Another
disadvantage of these polymers is that they are not always capable of
keeping the sunscreening agent within the capsule wall.
Encapsulation of actives by interfacial polycondensation is described in
U.S. Pat. Nos. 4,280,833 and 4,417,916. The actives thus formed have a
skin or thin wall of polyurea which improves release characteristics and
environmental stability. In the process, lignin sulfonate is used as an
emulsifier.
The use of lignin in controlled release of actives is also known in prior
art. The preparation of controlled release composites of lignin and
biologically active materials is described in U.S. Pat. No. 3,929,453 (Re.
29,238). The composites described are obtained by
coprecipitation-inclusion from an aqueous alkaline lignin solution, or by
the elimination of a common solvent from a lignin-biologically active
organic agent mixture. Preparation of reversibly swellable lignin gels is
described in U.S. Pat. Nos. 4, 184,866 and 4,244,729. The described gels
are formed by crosslinking lignin with epichlorohydrin and are able to
sustain the release of water-soluble and water-insoluble pesticides. The
use of other crosslinking agents such as formaldehyde and glutaric
dialdehyde is described in a related U.S. Pat. No. 4,244,728. The use of
said gels for UV protection, however, is not disclosed in any of these
patents.
The use of sunscreen agents in combination with encapsulation is described
in U.S. Pat. No. 4,844,896. Suggested sunscreen agents include methyl
orange, malachite green, methyl green and other colored dyes, and
suggested encapsulating agents include Eudragit L, Eudragit S, polyacrylic
acid and other polyacrylates. It is claimed that such systems keep the
sunscreen agent within the capsule. Incorporation of the sunscreen into
the capsule wall is not disclosed, however, and the problem of sunscreen
catalyzed degradation is not addressed.
The use of lignin or lignin in combination with polyacrylate materials as
an encapsulating agent is described in International Application No.
PCT/US92/03727. While lignin is disclosed as a sunscreen in this
application, the procedures used to make capsules are complex and require
a number of different chemicals.
The objective of this invention, on the other hand, is to incorporate
ultra-violet sunscreens, and more specifically sulfonated lignins,
sulfonated lignites, naphthalene sulfonates and other related compounds,
directly into the wall of the capsule. Chemical bonds keep the sunscreen
agents from diffusing out of the capsule where they are ineffective. A
further objective of incorporation of the sunscreen into the capsule wall
is to minimize sunscreen catalyzed degradation of sensitive actives.
Still another objective of the invention is to minimize the number of
ingredients needed in the encapsulation procedure, thereby simplifying the
overall process.
Other objectives and advantages of the invention will become evident on
reading the following detailed description.
SUMMARY OF THE INVENTION
The ultra-violet absorbing properties of lignosulfonates such as sulfonated
lignins derived from the sulfite pulping of wood or by sulfonation of
lignins derived from the kraft pulping of wood, sulfonated lignites
derived from the sulfonation of lignite coal, sulfonated tannins derived
by the sulfonation of bark tannins, synthetically prepared naphthalene
sulfonates and other related compounds are well established. The
functionality of the phenolic and other aromatic, carbonyl, catecholic and
carboxyl groups contribute to the ability of these types of compounds to
absorb UV light.
It has also been established that certain modifications such as high
temperature and other types of oxidation and/or azo-coupling as described
in U.S. Pat. No. 4,846,888 can significantly increase the absorbance of
these compounds particularly in the case of lignin sulfonates. It is also
well known that compounds of this type can effectively dissipate the
energy associated with the absorption of UV light internally thereby
preventing transfer to other proximate actives.
Under specific conditions sulfonated lignins and sulfonated tannins react
with proteins such as, but not limited to, gelatin to form insoluble
compounds. When crosslinked, these complexes have low solubility under
acidic or neutral conditions but are soluble in alkaline systems.
Also, under specific conditions proteins and carboxylated compounds such as
gum arabic interact to form complexes of limited solubility. This
interaction is the basis for microencapsulation of many pharmaceutical
materials.
In the present invention, a similar system is used to encapsulate
agriculturally active materials. The system employed in the present
invention, however, utilizes lignosulfonates (e.g. sulfonated lignin),
sulfonated lignite, sulfonated tannins, naphthalene sulfonates and/or
other related compounds in combination with a protein such as a high bloom
gelatin to form the capsule wall. The capsule wall formed by the
interaction of these materials is durable and has an ultra-violet
protectant as an integral part of its structure. The present invention
also has the advantages of requiring minimum mounts of chemicals to
produce, it is easy to use and the components of the cell wall are
non-toxic and environmentally safe.
BRIEF DESCRIPTION OF THE DRAWINGS
The drawings illustrate the best mode presently contemplated of carrying
out the invention.
In the drawings:
FIG. 1 is a graph of the percent degradation over time of parathion
encapsulated with a sulfonated lignin as the UV protectant;
FIG. 2 is a graph of the percent degradation over time of parathion
encapsulated with a sulfonated lignite as the UV protectant;
FIG. 3 is a graph of the percent degradation over time of parathion
encapsulated with an azo-lignosulfonate as the UV protectant; and
FIG. 4 is a graph of the percent degradation over time of parathion
encapsulated with a sulfonated lignin as the UV protectant as compared to
parathion emulsified with a sulfonated lignin in a non-encapsulated
formulation.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
It has been found that the UV sensitivity of agricultural actives including
chemical and biological actives can be greatly reduced by encapsulation
according to this invention. Such actives include any UV sensitive
synthetic, natural, or biologically derived pesticide. As used herein the
term "pesticide" has its normal connotation, and is intended to encompose
insecticides, herbicides, fungicides, rodenticides, molluscicides,
miticides, ovicides, algicides, larvacides, bactericides, and nematocides.
For example, the UV sensitive, agriculturally active agent might be a
biologically derived pesticide such as a virus, a bacterium, a nematode or
a fungi. Viruses include, but are not limited to, the nuclear polyhedrosis
virus (NPV) of the bullworm, Hellothis zea, of the gypsy moth Lymantria
dispar, of the Douglas fir tossock moth, Orgia pseudotsugata, of the
European pine saw fly Neodiprion sertifer or of Autographa californica or
of H. virescens. Bacteria known to be insecticidal agents, include but are
not limited to Bacillus thuringiensis, Bacillus Sphaericus, Bacillus
Popilliae and Bacillus Cereus may also be encapsulated. Examples of
possible nematodes include Neoaplectana carpocapsae, Octomyomermis
muspratti, Steinemema carpocapsae and Romanomermis culiciuora. Examples of
possible fungi include Verticillium lecanii and Entomophthora genus.
Chemical toxins include but are not limited to pyrethrum, a naturally
derived insecticide; pyrethroids i.e. synthetic copies of pyrethrum, such
as allethrin, cyfluthrin, cypermethrin, fenothrin, flucythrinate or
indothrin; and organophosphates, such as crufomate, dursban, dicrotophos,
parathion or phorate.
Any lignosulfonate, sulfonated lignite, sulfonated tannin or related
compound such as naphthalene sulfonates or condensed naphthalene
sulfonates or condensed naphthalene sulfonates can be used as a UV
protectant in the invention. These compounds are well known and are
derived from the sulfite pulping of wood, by sulfonation of lignins
derived from the kraft pulping of wood, by sulfonation of tannins derived
from wood barks, etc. The lignin materials used are typically in the salt
form (i.e. sodium, potassium, etc.). Preferable materials are those with
high molecular weight, strong absorptivities in the 290-400 nm wavelength
range and sufficient sulfonation to ensure reaction with the proteins
(e.g., gelatin, enzymes, etc.).
The lignosulfonates which may be utilized as the UV protectant materials in
the practice of and to obtain the novel protein/UV protectant complex of
the present invention are the treated or untreated spent sulfite liquors
containing the desired effluent lignosulfonate solids obtained from wood
conversion as the sulfite waste pulping liquor. These, as indicated, may
be utilized in the "as is" or whole liquor condition. They may also be
utilized as a purified lignosulfonate material from, or in which the
sugars and other saccharide constituents have been removed and/or
destroyed, or additionally inorganic constituents have been partially or
fully eliminated. Also sulfonated or sulfoalkylated kraft lignin can be
used as an adequate UV protectant material.
As used herein, the term "kraft lignin" has its normal connotation, and
refers to the substance which is typically recovered from alkaline pulping
black liquors such as are produced in the kraft, soda and other well known
alkaline pulping operations. The term "sulfonated lignin", as used in the
specification refers to the product which is obtained by the introduction
of sulfonic acid groups into the kraft lignin molecule, as may be
accomplished by reaction of the kraft lignin with sulfite or bisulfite
compounds, so that kraft lignin is rendered soluble in water. As used
herein, the term "sulfite lignin" refers to the reaction product of lignin
which is inherently obtained during the sulfite pulping of wood, and is a
principle constituent of spent sulfite liquor. The term "lignosulfonate"
(LSO.sub.3) encompasses not only the sulfite lignin, but also the
sulfonated lignin herein above described. Any type of lignosulfonate that
is hardwood, softwood, crude, or pure may be employed. Preferably,
lignosulfonates in their as is or whole liquor condition are employed. For
example calcium lignosulfonates, sodium lignosulfonates, ammonium
lignosulfonates, modified lignosulfonates and mixtures or blends thereof
may all be utilized herein. Lignosulfonates are available from numerous
sources in either aqueous solution or dried powder forms. For example
Lignotech USA, Inc. sells lignosulfonates under the trade designations
Lignosol, Norlig, and Marasperse which are appropriate for use in the
present invention.
As noted previously, napthalene sulfonates or condensed naphthalene
sulfonates may also be used as the UV protectant. Naphthalene sulfonates
are well known, and are typically synthesized via sulfonation of
napthalene, and napthalene condensates.
A number of proteins can be used along with the UV protectant to form the
capsule wall. Proteins such as an albumin, agar-agar, algen, gluten,
casein, fibrin or gelatin may be used as the protein source. The preferred
protein is gelatin with high bloom strengths as they give the strongest
capsule walls.
In the invention, the UV protectant and gelatin are dissolved in a neutral
to weak alkaline solution to prevent reaction. An agriculturally active
compound (e.g., an active chemical or biological pesticide such as a,
herbicide, insecticide, etc.) is then dispersed in or emulsified into the
mixture using standard dispersion/emulsification methods.
The pH of the resulting dispersion or emulsion is slowly lowered to between
6.5 and 8.0 by addition of dilute acid. Acids such as hydrochloric acid
(HCl), sulfuric acid (H.sub.2 SO.sub.4), nitric acid (HNO.sub.3),
phosphoric acid (H.sub.3 PO.sub.4) or acetic acid (CH.sub.3 COOH), may be
used to adjust the pH of the emulsion. When the pH reaches the isoelectric
point of the gelatin, positively charged groups capable of reacting with
negative charge groups on the UV protectant are generated. Coacervation
occurs resulting in capsule formation. If pH adjustment is desired,
caustic (NaOH) can be used to neutralize the resulting mixture.
Formaldehyde can also be added to harden (i.e., crosslink) the capsule
wall material. Other potential crosslinking agents in addition to
formaldehyde include acetaldehyde, glyceraldehyde, malonic acid dialdehyde
and glyoxal.
By varying the ratio of protectant and gelatin, the amount of protectant
introduced into the capsule wall can be varied. Capsule wall thickness can
be controlled by the addition rate of acid during coacervation.
Coacervation can also be effected by adding to the emulsion formed in
steps 1 and 2 a salt solution using salts such as Na.sub.2 SO.sub.4
(sodium sulfate), sodium citrate, sodium tartrate, sodium acetate or NaCl
(sodium chloride). Reference is made to U.S. Pat. No. 2,800,458 which
describes this technique.
EXAMPLE I
This example illustrates the general procedure for producing an
encapsulated agricultural active. One gram of high bloom gelatin was
dissolved in 95 grams of 40.degree. C. distilled water. Two grams of
sulfonated lignin (Lignosol SFX-65) was added to the gelatin solution and
the pH of the resulting mixture was adjusted to pH 6.5 with 0.1N HCl
Twenty grams of technical parathion was emulsified into the lignin gelatin
solution using a high shear mixer. While maintaining 40.degree. C with
stirring, the pH of the parathion emulsion was lowered to pH 5.0 by
further addition of 0.1N HCl. The mixture was then poured slowly into 300
grams of water containing 10 grams of 37% formaldehyde chilled in an ice
bath. The mixture was allowed to stir for 15 minutes and the pH was
adjusted to 6.5 with 0.5N NaOH.
EXAMPLE II
This example illustrates the UV protection imparted by the invention.
Samples of parathion encapsulated according the procedure described in
Example I were sprayed onto microscope slides. The slides were allowed to
dry and suspended equi-distant from the light source in a light box. A
lamp which produced a spectrum similar to that of natural sunlight was
used in the experiment. After certain time intervals, the slides were
removed and the samples were analyzed for remaining parathion content.
Control samples containing technical parathion only were run concurrently
with the samples. The results obtained indicated that degradation
resulting from exposure to simulated sunlight was significantly less in
the encapsulated samples with greater than 50% actives still available
after four weeks of continuous exposure (See FIG. 1).
EXAMPLE III
This example illustrates the effectiveness of a sulfonated lignite
protectant. Technical parathion was encapsulated with a combination of a
sulfonated lignite and high bloom gelatin as described in Example I and
exposed to simulated sunlight as described in Example II. Analysis of the
resulting exposed samples indicated UV protection similar to that obtained
with sulfonated lignin (See FIG. 2).
EXAMPLE IV
This example illustrates the superior effectiveness of an
azo-lignosulfonate protectant. An azo-lignosulfonate was prepared from
Marasperse CBOS-6 a sulfonated lignin product available from Lignotech
USA, Inc. and p-aminobenzoic acid using the methods described in U.S. Pat.
No. 4,846,888. Technical parathion was encapsulated with a combination of
a this azo-lignosulfonate and high bloom gelatin as described in Example I
and exposed to simulated sunlight as described in Example II. Analysis of
the resulting exposed samples indicated UV protection greater than that
obtained with either sulfonated lignin or sulfonated lignite (See FIG. 3).
EXAMPLE V
This example illustrates the superior effectiveness of encapsulation over
addition of lignosulfonate only. Technical parathion was encapsulated with
a combination of a sulfonated lignin (Marasperse CBA-1) and high bloom
gelatin as described in Example I and exposed to simulated sunlight as
described in Example II. Analysis of the resulting exposed samples
indicated UV protection much greater than that obtained using an
emulsified parathion non-encapsulated formulation containing an equal
amount of Marasperse CBA-1 (See FIG. 4).
Various modes of carrying out the invention are contemplated as being
within the scope of the following claims particularly pointing out and
distinctly claiming the subject matter regarded as the invention.
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